Herd immunity in Ireland is almost impossible without a vaccine

A vast global effort to develop a blend of drugs to control Covid-19 is under way

Science and in particular immunology – the study of how the body fights infections – is key to controlling Covid-19.

It will tell us why the virus causes severe disease in some individuals such as older people, obese people, men and diabetics and not in others.

Immunology is central to the design of vaccines and treatment approaches for a disease where the fatal outcome is a consequence of an over-active immune response to the virus.

Immunology will play a pivotal role in development and implementation of antibody testing.


The suggestion a level of herd immunity through Sars-CoV-2 infections is being built up in the community is not true

It is key to decisions being made to control the Covid-19 pandemic, and it is of great concern that there is no scientist and no immunologist on the near 40-member National Public Health Emergency Team.

Most, if not all, people hospitalised for Covid-19 develop antibodies against the virus as part of the body’s immune response to the infection. People with asymptomatic infections can also develop antibodies.

Despite reports of second infections in some individuals, there is no convincing scientific evidence that an individual can be re-infected with Sars-CoV-2 and this suggests that infection induces immunity, at least in the short term.

The testing for antibodies to identify individuals previously infected with Sars-CoV-2 will serve as an important adjunct to testing for the virus. It will provide crucial epidemiological data on the prevalence of the infection in the community; studies in other countries suggest that at least 5-15 per cent of the population have been infected.

Antibody testing, with reliable assays, will also identify those who have generated an immune response to the virus and may therefore be safe to return to work.

Induction of antibodies

Having antibodies against Sars-CoV-2 does not absolutely guarantee immunity from infection. However, this is the case with other viral infections and, indeed, induction of antibodies is the fundamental basis of all effective anti-viral vaccines in use today.

How close are we to a vaccine or to herd immunity?

Herd immunity is achieved when a critical threshold, usually 80-95 per cent of individuals in a target population (the herd) are rendered immune by previous infection or vaccination. It can provide protection for people who have not themselves developed immunity by eliminating the spread of the virus within the population and is particularly important in protecting the most vulnerable.

The immune system's attempt to eliminate the virus becomes uncontrolled resulting in severe inflammation in the lungs that spreads to other parts of the body

The suggestion that a level of herd immunity through Sars-CoV-2 infections is being built up in the community is not true. A community or country either has herd immunity or it does not.

A very optimistic figure of 60 per cent has been suggested as being the threshold for herd immunity against Covid-19, but this is not backed up by reproducible research findings. Estimates of 5-15 per cent of the population being infected are a long way off those required for herd immunity.

An effective vaccine is the safest and most effective means of generating herd immunity and is potentially the best medical intervention against Covid-19. More than 70 candidate Covid-19 vaccines are in development; seven of these have started the first of three phases of clinical testing. The University of Oxford Vaccine Group have predicted that they may a have a vaccine tested and ready for use in six months, but most scientists estimate it will take 12-18 months.

In order to achieve herd immunity, the entire population, including children, would have to be vaccinated. Therefore, vaccine manufacturers will have to satisfy regulatory agencies that the vaccine is not only effective but has passed stringent safety testing before it is licensed for widespread use.

Promising routes

Although there is no guarantee that the first vaccines will be effective, significantly, early studies in animal models are very encouraging and have suggested that certain candidate Covid-19 vaccines will be effective in humans.

How close are we to effective drugs for the treatment of Covid-19?

A huge international effort to develop drugs to control Covid-19 is ongoing.

The most promising of these is the anti-viral drug Remdesvir, which was granted an emergency use authorisation by the US Food and Drug Administration on May 1st. A report from China suggested treatment with remediation did not reduce deaths in patients with severe Covid-19. However, recent clinical trials in the US and Europe showed that the drug reduced the time of recovery from Covid-19 from 15 to 11 days.

Transfer of serum or antibodies from patients who have recovered from Covid-19 is another promising treatment approach. Plans to develop this treatment for Irish patients will be facilitated by immunology-based assays that will identify potential donors with high levels of antibodies that neutralise the virus.

In severe Covid-19, the immune system’s attempt to eliminate the virus becomes uncontrolled resulting in severe inflammation in the lungs that spreads to other parts of the body. This can manifest in a syndrome called a “cytokine storm”. Drugs that specifically block the activity of these cytokines are another treatment option. Although the first trials have been disappointing, clinical trials with alternative drugs are ongoing.

The antimalarial drug, hydroxychloroquine and the antibiotic azithromycin are being tested on the basis of their anti-inflammatory properties, but convincing data from controlled trials is still lacking.

Recent studies from Italy have shown that the inflammation associated with Covid-19 may promote blood clots leading to lung damage that may be potentially fatal. Therefore, drugs that prevent such thrombosis are being tested and may have therapeutic benefit.

In short, drugs that slow down virus replication, suppress severe inflammation and prevent thrombosis may form part of future combination approaches to combat Covid-19 disease. Scientists and clinicians are united in their efforts to identify optimum treatment strategies before an effective vaccine is developed.

Kingston Mills is professor of experimental immunology and academic director at the Trinity Biomedical Sciences Institute, Trinity College Dublin