O que é o teste de anticorpos para COVID-19 e devo fazer um?

What is a COVID-19 antibody test?

Em resumo, um COVID-19 antibody blood test pode ser usado para detectar anticorpos no seu sangue. Os anticorpos fazem parte do sistema imunológico e são criados para defender o corpo quando detecta infecções potencialmente prejudiciais (conhecidas como patógenos).

Em termos de coronavirus (COVID-19), the presence of antibodies suggests either or both of the following:

• You have previously been infected with COVID-19.

• Seu sistema imunológico respondeu produzindo anticorpos após ter o COVID-19 vaccine.

All vaccinations work by injecting a person with a modified or inactivated virus, or part of the virus, that they want to be protected against. When the immune system first meets a virus, it takes time to produce enough antibodies to defend the body effectively.

However, immunisation results in the production of B cells (a form of white blood cells) which make antibodies specific to a given infection. By triggering the production of antibodies without making the host ill, vaccinations mean that if a person does get infected with the virus, the immune system jumps to a 'secondary' response, which is much quicker and better at fighting the illness.

Além disso, tanto a imunização contra quanto a infecção por COVID-19 resultam na produção de outro tipo de imunidade - a imunidade de células T. As células T são um type of white blood cell que são amplamente eficazes na prevenção de doenças graves, em vez de infecções iniciais. A proteção das células T geralmente dura significativamente mais do que a imunidade por anticorpos.

It's important to note that a COVID-19 antibody test will not tell you:

• If you are currently infected with COVID-19.

• Whether you can still catch and spread COVID-19.

• The level of your T cells specific to COVID-19.

COVID-19 infection survey data

O teste de anticorpos está desempenhando um papel importante durante a pandemia de COVID-19. O Escritório de Estatísticas Nacionais (ONS) e o Departamento de Saúde e Assistência Social (DHSC) divulgam seus Coronavirus (COVID-19) Infection Survey data a cada quinzena. Esses dados fornecem uma análise importante sobre taxas de infecção e/ou vacinação passadas, com base em sujeitos amostrados aleatoriamente que testaram positivo para anticorpos.

How antibody swab testing can be useful

The COVID-19 Infection Survey is part of a major long-term study that tracks COVID-19 infections and vaccinations. It involves taking regular PCR swabs and antibody blood tests from over 596,000 volunteers across the UK, whether they have symptoms or not. This has helped to build a huge database that's used by scientists to better understand how COVID-19 immune response works.

Infection estimates

If a COVID-19 antibody test contributes to the national database, such as the COVID-19 Infection Survey, then it helps to improve estimations of the spread of past infections as well as response to vaccination.

Permanece uma diferença muito grande entre o número de pessoas testando positivo e o número real de pessoas que foram infectadas. Por exemplo, na semana que terminou em 1º de dezembro de 2021, o COVID-19 Infection Survey os resultados mostraram que 1,056 milhões provavelmente foram infectados naquela semana. Na mesma semana, 363,682 people had symptoms, took a PCR test and tested positive - três vezes menos que o número real de infecções. Mais testes de anticorpos ajudam a fechar essa lacuna de entendimento.

Vaccination estimates

By testing for COVID-19 antibodies, the COVID-19 Infection Survey is also painting a picture of the vaccination uptake and effectiveness. This includes estimates for how many vaccination doses a percentage of the general population has had in England. The survey has already shown a clear pattern between vaccination and testing positive for COVID-19 antibodies.

"Continuamos a observar um alto nível de anticorpos em todo o Reino Unido. Isso é provavelmente o impacto do booster programme com base em nossos dados, com grupos etários priorizados para reforços vendo aumentos nos níveis de anticorpos," diz a Dra. Rhiannon Yapp, estatística sênior.

Benefits of the London Medical Laboratory COVID-19 Antibody Blood Test

O Laboratório Médico de Londres Vacina COVID-19 e Resposta Imunológica - Teste de Anticorpos "Quantitativo" no Sangue can be used at home or in-store, and measures the level of immunoglobulin G (IgG) antibodies in your body.

Receiving a positive result means that the test has detected an arbitrary units per millilitre (AU/ml) level of above 50 units, suggesting that you have either been exposed to COVID-19 or that your body has produced an immune response to the vaccine.

This said, it is possible to have an immune response with a lower level of antibodies than this. Therefore, a negative result does not mean that you haven't been infected or that your vaccination hasn't worked. Whether you receive a positive or a negative result, it's important to note that the COVID-19 antibody test doesn't paint a full picture of your immunity.

No entanto, acredita-se que 1 in 100 people não produzem anticorpos após a vacinação contra a COVID-19. O Dr. Quinton Fivelman, diretor médico do London Medical Laboratory, também destaca que: "Pesquisas recentes mostraram que a resposta imunológica inicial em pessoas que foram vacinadas contra a COVID-19 can predict the level of protection they will have to the virus over time."

A positive result from the COVID-19 antibody test kit can confirm if you have produced detectable antibodies in response to the vaccine. Most importantly, this can provide you with peace of mind to know you have some level of protection through them.

Limitations of the London Medical Laboratory COVID-19 Antibody Blood Test

While testing positive for antibodies can provide you with peace of mind, testing negative is not a reason to panic about your immune protection against COVID-19.

Professor Rodney E. Rohde, a professor of clinical laboratory science and an infectious disease specialist at Texas State University, stresses that anyone who chooses to take an antibody test "truly needs to 'understand' what these results might mean".

Antibodies are not a precise measure of immunity

It's important to draw the distinction between having immunity against COVID-19 and testing positive for IgG antibodies. Antibody levels can vary from person to person and having levels below an AU/ml level of above 50 units is not the same as having no immune protection.

"A low level of IgG may also not mean one it not completely vulnerable to the virus. The test does not measure T-cell activity and other forms of protection," says Rohde.

Tanto as células B quanto as células T (conhecidas como linfócitos) são involved in our immune response às infecções. As células B produzem anticorpos, enquanto as células T atacam diretamente o patógeno invasor e estão associadas à imunidade de longo prazo.

Ainda não se sabe quanto tempo os anticorpos duram ou por quanto tempo seus níveis de IgG permanecem altos após a infecção ou vacinação, e pesquisas isso está em andamento.

These measurements may not be suitable for all virus variants

The London Medical Laboratory COVID-19 antibody test is a quantitative measurement of IgG antibodies against the spike receptor binding domain (RBD) of COVID-19. The RBD is the part of the virus that allows it to lock on to body receptors to gain entry into body cells. Rohde advises that this specific binding domain may not be the best measurement for future COVID-19 variants, such as when we learn more about Omicron.

At-home sampling errors

Kits de teste em casa podem ser convenientes, mas Rohde também aponta que erros de amostragem podem ocorrer se as instruções não forem seguidas conforme indicado. Pesquisa estudos demonstraram que a maioria dos erros laboratoriais ocorre na fase pré-analítica (a coleta e armazenamento dos exames de sangue).

Use of data for research

While a COVID-19 antibody test for the ONS/DHSC Infection Survey feeds into a database that scientists can access in order to gain greater understanding of COVID-19 immunity, private test kit results are not available for scientific research. This is, however, an area that London Medical Laboratory is looking into.

For now, the benefit of ordering an antibody test for COVID-19 will be for your own peace of mind and curiosity.