On January 16, India started its vaccination drive against Covid-19, administering preliminary doses to nearly 2,00,000 healthcare workers, and reminding them to come back on February 13 for their second shots. But when that date rolled around, fewer than 8,000 returned – a measly 4% of the total.

By February 15 morning, the proportion had improved, but only just: 24,561 healthcare workers got their second shot out of the 2,24,301 who ought to have received it, or just over 10%.

This is a problem – and not just for India. If people skip their second doses, or even if they delay the doses beyond the recommended time frame, it gives the coronavirus more chances to re-arm itself – to mutate by chance in a way that could lend it high resistance to the vaccines we have. If that mutant, resistant form spreads, a year’s worth of vaccine research could be overwhelmed by a fierce new wave of disease.

Experience from TB

This scenario echoes another that has already transpired with tuberculosis. India has become a cradle for strains of Tuberculosis bacteria that can hold out against antibiotics. In 2019, the country registered the highest number of drug-resistant TB cases in the world.

Among the reasons that bacteria grow inured to antibiotics is an insufficient duration of treatment: doctors prescribing regimens that are too brief, or patients stopping their doses if they feel better or cannot afford their medicines. These strains of drug-resistant TB bacteria have spread to the US, the UK, Germany and other countries. Crafting new antibiotics to battle these bacteria is difficult as well as expensive: 10 years to 15 years of work and at least $1 billion in investment per drug.

On February 22, India will start rolling out its vaccines to the general populace. In a country like India, there are plenty of reasons why people may skip their second doses. Perhaps they will not find transport to a clinic on the day, or will have to work for a day’s wages instead. Perhaps they will feel an adverse reaction after the first dose and decide they do not trust the vaccine.

It is arguably the responsibility of health authorities to convey the importance of taking both doses, and to track those who have neglected their follow-up visits. If the numbers of second doses administered are so low even among healthcare workers – who, presumably, can be mandated to take their doses, work in hospitals or clinics where the vaccine can be administered, and understand the need for the second shot – authorities will have to step up the urgency of their communication even further.

The coronavirus is still around, and unless it is stopped dead in its tracks by a comprehensive immunisation campaign, it will keep spreading. Viruses mutate in warm bodies. India has 130 crore of them.

This article first appeared on Quartz.