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Antibody testing could lend a hand to global vaccine programs crippled by COVID-19

Authors: Simon Mutembo and Naor Bar-Zeev

COVID-19, the most significant global pandemic since 1918, has overwhelmed the attention of most political and public health leaders over the past year. But people are still getting sick from the conditions that harmed and killed them before COVID-19 came into our lives. 

In fact, according to new estimates from the World Health Organization (WHO) and U.S. CDC, 207,500 children died from measles in 2019. And 89,000 more succumbed to pertussis, or whooping cough, in the same year. 

That’s because, even before the pandemic, safe and effective vaccines for measles, pertussis, and other diseases were not reaching tens of millions of children. Intermittent mass campaigns often don’t reach all children missing out on routine vaccination.

To help plan for the delivery of vaccines to millions of individuals missed during routine vaccinations, we need a deeper understanding of population immunity, which includes antibody testing and serosurveys—public health investigations that integrate the collection and analysis of blood samples to detect antibodies in a particular population.

Here’s where we stand at the moment: more antibody testing is going on than ever before. Population-level antibody levels have shed light on COVID-19 outbreaks, especially where testing for current infections has been limited. Many scientists thought that antibody testing would definitively prove if people had previously been infected with COVID-19 and whether they had immunity. Countries even considered giving immunity passes for travel during lockdowns.

But antibody testing has not been that magic bullet. In Spain and New York—despite huge outbreaks and thousands of deaths—testing showed that barely a quarter of the people tested had antibodies to SARS-CoV-2. Antibodies to SARS-CoV-2 appear to decline rapidly after an infection, especially in people who experienced mild cases.

Still, antibody testing has provided critical information in large populations. For example, positivity rates from Indian cities such as Delhi, Mumbai, and Pune show that outbreaks were larger than earlier suspected.

Photo of Mumbai crowds in pre-Covid times by Eric Parker

Antibody testing for COVID-19 has been crucial for a second reason: it documents the spread of disease in people with mild symptoms.

We need to scale up antibody testing not only for COVID-19, but for vaccine-preventable diseases generally. With vaccine programs globally struggling to catch up with people who have missed vaccine doses during lockdowns, there are likely large numbers of children susceptible to measles and other common diseases that threaten lives. In the Philippines, immunization coverage dipped so low that 2.4 million children are susceptible to measles. Even in countries not as impacted by COVID-19, the number of children susceptible to measles has increased. For instance, in Zambia the number of children prone to the disease—already in the hundreds of thousands before the pandemic—increased considerably in the first half of 2020.

Zambia also provides good news, however, by highlighting the power of serosurveys as a tool for monitoring disease and ultimately preventing severe illness and saving lives. For example, serosurvey results revealed that an unexpected number of young women of childbearing age in Zambia were not protected against rubella, while in this same population children and adults were adequately protected against measles (see chart).

One solution would be to integrate measles serosurveys with large antibody surveys for SARS-CoV-2. Combining serosurveys for different antibodies has technical challenges. We need different sampling frames because people getting tested for SARS-CoV-2 antibodies are often not age-eligible for measles vaccination. But these challenges are outweighed by the need to protect the millions of children who are vulnerable to measles.

Results could help governments target catch-up campaigns to save lives and avert health spending on preventable diseases. Integrating serosurveys with coverage surveys after a mass vaccination campaign—which countries are already launching to claw back progress lost earlier this year—has been shown to be more efficient than standalone serosurveys.

More antibody testing for SARS-CoV-2 is needed as well. Rapid and repeated testing might be possible with at-home self-testing, which can help monitor disease activity. COVID-19 vaccines will initially be in short supply and serosurveys could help with vaccine targeting.  

As lockdowns ease, countries must anticipate outbreaks of vaccine-preventable diseases in 2021. As we continue to rightly fear COVID-19, we must act far more aggressively to use all available tools, like antibody testing and serosurveys. They are imperfect instruments, but they still offer great promise for protecting both adults and children from disease, be it COVID-19, measles or others that profoundly affect our lives.

Simon Mutembo MBCHB, MPH, Ph.D., is an International Vaccine Access Center (IVAC) scientist at the Johns Hopkins Bloomberg School of Public Health’s Department of International Health where he serves as co-investigator on the Strengthening Immunization through Serological Surveillance (SISS) project being implemented in Zambia and India. Earlier, Mutembo served in various clinical practice and public health leadership roles in the Ministry of Health of Zambia.

Naor Bar-Zeev, MBBS, MPH, MBiostat, Ph.D., deputy director of the International Vaccine Access Center (IVAC) at the Johns Hopkins Bloomberg School of Public Health, is a pediatric infectious diseases physician and statistical epidemiologist working in global child health across East Asia, the Pacific, and Africa

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